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What you need to know about anal cancer

Anal cancer occurs in the anus, located at the end of the gastrointestinal tract. It is different from and less common than colorectal cancer, which is cancer of the colon or rectum.

Anal cancer is rare, but the number of new cases is rising. According to the American Cancer Society, in 2017, there are likely to be about 8,200 new cases, of which 5,250 will affect women and 2,950 will affect men. Around 1,100 people are expected to die from anal cancer, including 650 women and 450 men.

Various risk factors are linked to anal cancer, but infection with two types of the human papilloma virus (HPV) appear to underlie 79 percent of cases.

Anal cancer is rare before the age of 35 years. The average age of diagnosis is in the early 60s. Men have a 1-in-500 chance of getting anal cancer, and the risk is slightly higher in women.

women may experience lower back pain as the tumor presses on the vagina

women may experience vaginal dryness

Causes

In anal cancer, a tumor is created by the abnormal and uncontrolled growth of cells in the anus.

The anus is the area at the very end of the gastrointestinal tract. The anal canal connects the rectum to the outside of the body. It is surrounded by a muscle known as the sphincter. The sphincter controls bowel movements by contracting and relaxing. The anus is the part where the anal canal opens to the outside.

The anal canal is lined with squamous cells. These flat cells look like fish scales under the microscope. Most anal cancers develop from these squamous cells. Such cancers are known as squamous cell carcinomas.

The point at which the anal canal meets the rectum is called the transitional zone. The transitional zone has squamous cells and glandular cells. These produce mucus which helps the stool, or feces, pass through the anus smoothly.

Most anal cancers are squamous cell carcinomas, but adenocarcinoma can also develop from the glandular cells in the anus.

Risk factors

Multiple risk factors have been studied that are linked to anal cancer. They include any or a combination of the following:

Human papilloma virus (HPV): Some types of HPV are closely linked to anal cancer. Around 79 percent of people with anal cancer have HPV 16 or 18, and 8 percent have other types of HPV.

Multiple sexual partners: This activity increases the risk of contracting HPV, which, in turn, increases the risk of anal cancer, which is a known risk factor.

Receptive anal intercourse: Men and women who receive anal intercourse have a higher risk of developing anal cancer. Men who are HIV-positive and who have sex with men are up to 90 times more likely to develop anal cancer, compared with the general population.

Other cancers: Women who have had vaginal or cervical cancer, and men who have had penile cancer are at higher risk of developing anal cancer. This is also linked to HPV infection.

Age: Anal cancer, like most cancers, are more likely to be detected at an older age.

A weakened immune system: People with HIV or AIDS and those who are taking immunosuppressant medications after a transplant are at greater risk.

Smoking: Smokers have a significantly higher risk of anal and other cancers than non-smokers.

Treatment

Treatment for anal cancer will depend on various factors, including how big the tumor is, whether or not it has spread, where it is, and the general health of the patient. Surgery, chemotherapy, and radiation therapy are the main options.

Surgery

The type of surgery depends on the size and position of the tumor.

Resection

The surgeon removes a small tumor and some surrounding tissue. This can only be done if the anal sphincter is not affected. After this procedure, the person will still be able to pass a bowel movement.

Abdominoperineal resection

The anus, rectum and a section of the bowel are surgically removed, and a colostomy will be established. In a colostomy, the end of the bowel is brought out to the surface of the abdomen. A bag is placed over the stoma, or the opening. The bag collects the stools outside the body. A person with a colostomy can lead a normal life, play sports, and be sexually active.

Chemotherapy and radiotherapy

Most patients will probably need chemotherapy, radiation therapy, or both.

Radiation therapy may be combined with chemotherapy to destroy anal cancer cells. Treatments may be given together or one after the other. This approach increases the chance of retaining an intact anal sphincter. Survival and remission rates are good.

Chemotherapy uses cytotoxic drugs that prevent the cancer cells from dividing. They are given orally or by injection.

Radiotherapy uses high-energy rays that destroy the cancer cells. Radiation can be delivered internally or externally.

Radiotherapy and chemotherapy have adverse effects, and combining them may make the side effects more acute.

Outlook

Cancer is diagnosed according to its stage. Treatment options and outlook depend on the stage at which it is diagnosed.

A common way of staging cancer is from 0 to 4. In stage 0, the cancer cells are only in the top layer of the anal tissue. This is also known as Bowen disease. At stage 4, the cancer has spread throughout the body.

The chance of surviving another 5 years or more after diagnosis depends on the stage and on the type of cancer.

It is important to remember that these figures are based on average rates from the past. As medicine progresses, the expectation is that treatments are increasingly effective, especially if the cancer is diagnosed at an early stage.

The outcome also depends on a person's age and health condition apart from the cancer.

Diagnosis

A doctor will ask about the symptoms and medical history, and carry out an examination.

If the doctor believes anal cancer is present, they will refer the patient to a colorectal surgeon, a doctor who specializes in bowel conditions.

The specialist may carry out a number of tests.

A rectal examination

This may be uncomfortable, but it is not usually painful. The doctor may use a proctoscope, anoscope, or sigmoidoscope to examine the area in more detail. The examination will determine whether a biopsy is needed.

A biopsy

A small sample of tissue is taken from the anal area and sent to the lab for testing. Tissue will be examined under a microscope.

If the biopsy reveals cancerous tissue, further tests will be done to find out how large the cancer is and whether it has spread.

A CT, MRI, or ultrasound scan can help confirm the results. This may be a rectal ultrasound, where the instrument is inserted into the anus.

Prevention

Anal cancer is rare, but some recommendations can help reduce the risk further.

These include:

reducing the chance of being infected with HPV through vaccination

use condoms when having sex

limiting the number of sexual partners

abstaining from anal intercourse

not smoking

Most cases of anal cancer can be diagnosed early. However, if symptoms start higher up in the anal canal, this might not be possible.

People who have a higher risk should consider screening for anal cancer. This includes women who have had vulvar or cervical cancer, known HPV infection, anyone who is HIV positive, those with a history of anal warts, and recipients of an organ transplant.

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